This invention relates to parameter measuring systems. The invention more particularly relates to automated systems for remotely reading out analog meters.
Parameter measuring systems allow users to gain information representative of a sensed parameter. The sensed parameters may be voltage, current, fluidic flow or other quantities to be measured. The read-out device employed in a parameter measuring systems may be, for example, a digital meter or an analog meter.
Many conventional automated parameter measuring systems employ digital meters. Digital meters generally allow users to visually read information representative of the sensed parameter by digitizing the sensed parameter and producing a numerical display representative of the digitized information.
Many digital meters include outputs allowing the digitized information to be transmitted and remotely read. A parameter measuring system for remotely reading digital meters eliminates the need for a user to read the information at the meter (in a possibly hazardous environment), and enter the information into an information processing system, such as a computer.
For parameter sensing systems utilizing analog meters, the analog meters generally include a movable pointer disposed over a stationary scale. The needle is adapted to be deflected in proportion to a sensed parameter, such as electric charge, voltage, or current. Analog meters are designed specifically for users to visually read information representative of a sensed parameter.
Most analog meters either provide no output other than the visual display or provide an analog output signal representative of the displayed information. In the latter case, additional circuitry is usually required to convert the analog signal to a form suitable for use by an information system such as a computer. Often the analog signal also cannot be transmitted any significant distance without additional drive circuitry.
By including this additional circuitry, one could construct an automated system for remotely reading out analog meters which provide analog output signals. However, a prior art analog meter which provides no such output signals cannot currently be used to construct an automated system for remotely reading out data from the analog meter.
In order to accommodate automated systems, some analog meters may be replaced by more expensive digital meters having similar input characteristics, but which also provide digital output signals. However, certain analog meters cannot be so replaced because of the technique they employ for converting a sensed parameter into displayed information representative of the sensed parameter.
The conversion technique employed, for example, in certain voltmeters is electrostatics. Electrostatic voltmeters operate on the principle that like charges repel. This principle is used in repelling a movable indicator, which is under tension from a spring, away from a stationary reference point. The movable indicator is used to display information representative of the sensed voltage, since the amount of indicator movement is directly dependent on the applied voltage signal.
An important characteristic of electrostatic voltmeters is that they have very high input impedances. As a consequence of the high input impedance, the voltage signal being measured is not degraded by the presence of the voltmeter. It is also important that such voltmeters respond quickly to a sensed voltage signal. Electrostatic voltmeters respond very quickly because they present an input impedance of effectively infinite resistance and a very small capacitance.
There are some voltage measurements which must be performed by voltmeters with a very high input impedance. There are also some current measurements which must be performed by ammeters with a very low input impedance. In both cases above this is because the precise value of the input signal must be maintained with as little degradation as possible.
Certain high voltage power supplies generally have very high output impedances because they provide very little current. Such power supplies might be used to drive a flashlamp, or might be used for an image converter or intensifier tube. Performing voltage measurements on these power supplies is difficult because of this high output impedance. For example, to obtain less than 0.1 percent error, the measuring device must have an input resistance that is 100 times greater than the output resistance of the high voltage power supply being tested.
For all of these examples, operator-read analog meters have been used in the prior art to perform such measurements. It is an object of the present invention to provide a parameter measuring system for remotely reading out analog meters. Certain measurements, such as measuring the voltage of a high voltage-low current power supply, cannot be performed utilizing conventional techniques.
It is another object to provide an automated system for remotely reading out analog meters, eliminating the requirement of having a user enter the information into an information system.